In the semiconductor process, a vertical heat-treating apparatus is known as a batch type processing apparatus. The batch type processing apparatus heat-treats a large number of semiconductor wafers at once by, e.g., oxidation, diffusion, annealing, and CVD. In the vertical heat-treating apparatus, a large number of wafers are arrayed and held at predetermined gaps in the vertical direction in a holding tool called a wafer boat. This holding tool is loaded into a vertical process chamber. The wafers are heat-treated while being heated by a heating mechanism disposed around the process chamber.
As a process which forms a silicon oxide film (SiO2 film) by oxidizing a silicon wafer, a dry oxidation process and wet oxidation process are known. In the dry oxidation process, oxygen (O2) gas and hydrogen chloride (HCl) gas are supplied to the process chamber. In the wet oxidation process, water vapor and oxygen gas are supplied to the process chamber. The dry oxidation process and wet oxidation process are selected in accordance with the target film quality.
In the dry oxidation process, a silicon wafer and layer are oxidized by the oxygen gas, while surface impurities are removed by the gettering effect of chloride. More specifically, for example, a large number of wafers are held like shelves by a wafer boat, and are loaded in a vertical process chamber. A processing atmosphere with a predetermined temperature is formed in the process chamber. Subsequently, oxygen gas and hydrogen chloride gas are supplied at room temperature into the process chamber from its ceiling, and are exhausted from the lower side.
The wet oxidation process requires an external combustor outside the process chamber. Part of the oxygen gas and the hydrogen (H2) gas are burned by the combustor to generate water vapor. The remaining oxygen and water vapor are supplied into the process chamber.
As another heat treatment, an oxinitriding process is known. According to the oxinitriding process, dinitrogen monoxide gas (N2O gas) is introduced at room temperature into the process chamber. The introduced gas reacts with the silicon layer of the wafer to form a silicon oxide film (silicon oxinitride film) containing nitrogen.